Tririga Inc. was already growing quickly before September when it started selling a suite of computer programs to help companies quantify and cut energy use related to buildings.

Then things took off for the 10-year-old maker of real estate management software.

In the past six months, Tririga has signed up a dozen companies for an average of $1 million each for software and professional services related to its green building initiative.

“It’s just on fire,” said Tririga CEO George Ahn from the company’s office in Pleasanton.

The new product — called TREES (Tririga Real Estate Environmental Sustainability) — accounted for nearly 30 percent of Tririga’s fourth quarter revenue. The company’s annual revenue was estimated at $50 million to $60 million for 2008. Total revenue has been increasing an average of 30 percent annually for several years.

Tririga, which has 225 employees, hired about 40 people last year and expects to hire an equal number by the end of 2009. The company has most of its executives in Pleasanton, as well as offices in Las Vegas, where it was founded in 2000, and Philadelphia.

The company has applications for managing real estate construction, maintenance, financing, space allocation and even moving of offices.

Customers include 40 percent of the Fortune 100, and include names such as General Electric, Pfizer and Gap Inc., as well as local, state and federal government agencies, Ahn said.

Daniel O’Toole, a Washington, D.C., software analyst, said that Tririga was “ahead of the curve” in its real estate sustainability initiatives. The depth of demand will likely be huge, he said.

“Tririga is the definite leader in the space, and they’re the most innovative,” O’Toole said.

The overall market for real estate portfolio management software is nascent but growing, said O’Toole. Competitors include Manhattan Software, Planon System Solutions, Archibus and FM:Systems, he said.

Ahn said TREES lets companies with vast real estate portfolios show maps of their facilities and drill down on any one building to present tangible proof of what the company has done to reduce emissions at specific sites.

“The problem for corporate America is they don’t know what their carbon emissions are. They also have no idea what their target should be, and they don’t know how to get there,” he said.

An early adopter of the TREES program was Nokia, the Swedish mobile phone giant.

“Tririga gives us the tools we need to collect and report on all of our environmental data and has helped us launch a full-scale, global program to act on the best opportunities to improve our environmental sustainability,” said Robert Fitzgerald, Nokia’s global director of process, tools and reporting, in a statement.

And this month, the Denver Public Schools system in Colorado said it would use TREES to measure, manage and reduce greenhouse gas emissions for over 180 school facilities.

Tririga also stands to gain indirectly from the federal stimulus package. The Michael Baker Corporation, a large engineering and consulting firm, is showing customers how to use TREES to take advantage of $20.5 billion in appropriations for government agencies that have green construction projects and invest in energy efficiency.

Stephen Stokes, vice president of sustainability and green technology at AMR Research, said that organizations can typically save 20 to 40 percent on their real estate operations costs with Tririga.